The widely-used input device of a computer includes for example a mouse device, a keyboard device, a trackball device, a touchpad device, or the like. Among these input devices, the mouse device is the most prevailing because it is very easy-to-use for most users. When a mouse device is held by the palm of a user, the user may move the mouse device to control the movement of a cursor shown on a display screen of a computer.
Hereinafter, the structure and the function of a conventional mouse device will be illustrated with reference to FIG. 1. FIG. 1 schematically illustrates the connection between a conventional mouse device and a computer system. The computer system 2 comprises a computer host 21 and a display screen 22. The computer host 21 is in communication with a mouse device 1 and the display screen 22. The computer host 21 has a connecting port 211. A graphic-based window 221 and a cursor 222 are shown on the display screen 22. The mouse device 1 is used for controlling the cursor 222 to have the computer host 21 execute a corresponding command. The mouse device 1 comprises a main body 10, a left button 11, a right button 12, a scroll wheel 13, and a connecting cable 14. The left button 11 is disposed on the main body 10 and located at a left side of the scroll wheel 13. In addition, the left button 11 is exposed outside the main body 10. By pressing down the left button 11, a left button signal is generated. Like the left button 11, the right button 12 is disposed on the main body 10 and located at a right side of the scroll wheel 13. By pressing down the right button 12, a right button signal is generated. The scroll wheel 13 is disposed within the main body 10 and partially exposed outside the main body 10. By rotating the scroll wheel 13, a corresponding scrolling signal is generated. The connecting cable 14 is connected with the main body 10 and protruded outside the main body 10. When the connecting cable 14 is connected with the connecting port 211, the communication between the mouse device 1 and the computer system 2 is established.
The inner structure of the conventional mouse device will be described as follows. FIG. 2 is a schematic cross-sectional view illustrating the structure of the conventional mouse device. The main body 10 of the mouse device 1 is placed on a working surface T. The inner portion of the mouse device 1 comprises a main board 15, a sensing module 16 and a controlling unit 17. The sensing module 16 is disposed on the main board 15 and partially exposed to a bottom opening 101 of the main body 10. The sensing module 16 comprises a light-emitting element 161, an optical assembly 162 and an optical sensor 163. The light-emitting element 161 is disposed on the main board 15. Moreover, the light-emitting element 161 emits a light beam B. The optical assembly 162 is disposed within the main body 10. After the light beam B passes through the optical assembly 162, the light beam B is refracted by the optical assembly 162. Consequently, the light beam B is projected onto the working surface T, which is disposed under the main body 10. After the light beam B reflected by the working surface T is received by the optical sensor 163, a displacement signal is generated by the optical sensor 163 according to the light beam B. The control unit 17 is disposed on the main board 15 and electrically connected with the optical sensor 163.
The method of generating the displacement signal will be described as follows. When the mouse device 1 is placed on the working surface T but not moved, the light-emitting element 161 emits the light beam B. After the light beam B passes through the optical assembly 162, the light beam B is refracted by the optical assembly 162. Consequently, the light beam B is projected onto the working surface T. Then, the light beam B is reflected to the optical assembly 162 by the working surface T. After the light beam B passes through the optical assembly 162, the light beam B is received by the optical sensor 163. Meanwhile, the optical sensor 163 generates a first working surface image. When the mouse device 1 is placed on the working surface T and moved to a specified position, the light beam B from the first light-emitting element 161 is guided to the optical sensor 163 by the optical assembly 162, the working surface T and the optical assembly 162 sequentially. Meanwhile, the optical sensor 163 generates a second working surface image.
Then, the controlling unit 17 receives the first working surface image and the second working surface image from the optical sensor 163. According to the result of comparing the first working surface image with the second working surface image, the controlling unit 17 acquires a displacement amount of the main body 10 relative to the working surface T and generates a displacement signal according to the displacement amount. That is, when the mouse device 1 is moved on the working surface T, the sensing module 16 detects the displacement amount of the main body 10 relative to the working surface T and generates the displacement signal according to the displacement amount. After the displacement signal is received by the computer host 21, the movement of the cursor 222 on the display screen 22 is controlled by the computer host 21 according to the displacement signal.
With increasing development of mouse devices, the functions of the mouse devices are gradually increased. For example, the moving resolution of the mouse device is largely increased. The moving resolution of the mouse device denotes the sensitivity of moving the cursor of the computer host when the mouse device is moved for a certain distance. As the moving resolution is increased, the sensitivity of moving the cursor is increased. When the mouse device is used to operate the computer game, it is necessary to move the mouse device quickly. That is, the higher moving resolution of the mouse device is required. When the mouse device is used to perform a document processing task, the lower moving resolution of the mouse device is required. For preventing the user from frequently changing the suitable mouse device, a mouse device with a changeable moving resolution has been introduced into the market. This mouse device has a switching element for changing the moving resolution of the mouse device in response to the pressing action of the user. When the switching element is pressed down once, the moving resolution of the mouse device is changed. For example, the moving resolution is changed from 800 dots per inch (dpi) to 1600 dpi. When the switching element is pressed down again, the moving resolution is changed from 1600 dpi to 800 dpi. In other words, the moving resolution of the mouse device is changeable.
Although the moving resolution of the mouse device is changeable, there are still some drawbacks. For example, this mouse device cannot be applied to all kinds of working surfaces. In case that the working surface is made of a transparent material (e.g., acrylic resin), the light beam is transmissible through the working surface. Since the reflected portion of the light beam is reduced, the efficacy of generating the displacement signal is adversely affected.
Therefore, there is a need of providing a mouse device that has the adjustable moving resolution and is applicable to various working surfaces.